[etherlab-users] Jitter when trying to use EtherLab Master at hard real-time 1 kHz under RT-PREEMPT

[Matthieu Bec]

Hello Soo-Hyun Yoo,

Here I have RT_PREEMPT (3.0.8-rt23), we dont use the ioctl interface as 
provided by ethercat master, but a similar scheme so I was curious...
Anyways, setting up a simple mini-usr-rt.c that *does* use the etherlab 
API was easy - a simple digital-out square wave @1kHz (2000Hz bus 
speed), signal checked on a scope, shows very little jitter - 1us. or less.

Regards,
Matthieu


On 03/05/12 15:59, Soo-Hyun Yoo wrote:
> My tenuous understanding of this is that since the EtherCAT character
> device tries to use the kernel's ioctl calls, the kernel's ioctl
> "interface" (?) needs to be patched. Since RT_PREEMPT is the only patch
> that does so, while LXRT provides its own interface, the former is the
> only one capable of real-time user space operation while the latter is
> limited to kernel space. Based on this assumption, I am hoping that the
> EtherLab Master is capable of real-time operation in user space under
> RT_PREEMPT.____
>
> __ __
>
> What can I do to lessen this jitter? Does anyone have a working EtherCAT
> master running at 1 kHz with jitter under 50 us?
>


-- 
Matthieu Bec                GMTO Corp.
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